Nicene and Ante-Nicene Fathers, Ser. II, Vol. XIV:The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XXXIII

The underlying principle of this canon is the same as the last, for as the receiving of p. 150the Eulogiæ which were sent by heretics as a sign of communion, signified a communion with them in religious matters, so the sharing with them common prayer is a declaration of the same communion, and therefore to be avoided. This is also set forth in Apostolical Canon number xlv.